Congress actually passed the Metric Conversion Act in 1975, which was supposed to switch us over to the Metric system. But they didn't specify a time limit for the conversion, and the whole effort fell apart.
Interesting article here:
<a href=http://ts.nist.gov/ts/htdocs/200/202/lc1136a.htm target=new>http://ts.nist.gov/ts/htdocs/200/202/lc1136a.htm</a>